Granules of agglomerative powders



May 5,1936. E. BILLINGS ET AL GRANULES OF AGGLOMERATIVE POWDERS OriginalFiled Aug. 12, 193

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Patented May 5, 1936 UNITED STATES PATENT orrlcs' 2,039,766 GRANULES orAGGr oMEmnvn" POWD ' Massachusetts Original application August 12,1933.- Serial No. 684,884. Divided and this application April 19,

1934, Serial No. 721,382

2 Claims. (01. 134- 58) This invention relates to a novel product madefrom fine dry powders as a result of processes of mechanical treatmentsolely. In general it applies to the broad field of solid substanceswhich derive their applications in the arts and sciences from their finestate of subdivision. Thisextreme degree of fineness carries theinevitable and generally undesirable concomitant of dustiness, and thisdustiness, arising from the minute weight .of the individual particle,may lead to serious undesirable commercial consequences; for example,contamination of other nearby products and processes, excessivedeterioration of fixtures, ma-

chinery and furnishings and respiratory and other occupational disordersin the workmen exposed to the dust.

We have discovered that certain powdered materials of this type may beagglomerated on themselves, by purely mechanical treatment,

without the assistance of binders, solvents, liquids, tars, or theaddition, either temporarily or permanently, of any foreign substance.The agglomerates formed by our process are of greater apparent densityin bulk than the loose powders 5 from which they are formed and consistof more or less spherical masses having such a high ratio of weight tosurface that they are not dusty. Also, they have smooth, polished,non-adherent surfaces and compact, adhesive internal struc- 30 tures.These characteristics give the resulting agglomerates a free-flowingnature which materially simplifies handling in bulk, homogeneous mixingwith other materials, delivery by gravity through chutes and pipelines,packaging in any 3.; desired weight, and all of the other conveniencesimparted to the product by its extreme fluidity and dustlessness.

One important field of use for our invention is the carbon blackindustry, for example, in con: 40 nection with the so-called "chanhelcarbon black produced by burning natural gas flames against metallicsurfaces. particle is so small that its shape and exact size are beyondmicroscope determination. As

45 first produced, such carbon black has an apparent density in bulk ofabout three pounds per cubic foot. It has been the practice to increasethis apparent density in bulk to about twelve pounds per cubic foot bystirring and then to increase it 50 further to about twenty-five poundsper cubic foot by compressing. The resulting compressed carbon black dueto its dusty nature is still inconvenient to handle because it soreadily reverts to its dusty form. In addition to this, the difficulties55 of packaging carbon black by compression have The ultimate carbonblack necessitated the employment of small sacks, twenty-five pounds orlessln capacity, and for practical reasons the industry has been obligedto standardize on two sizes of sacks.

We have found that by subjecting the carbon 5 black of commerce tocertain conditions of turbulent pressure, the fine dusty particles ofwhich it is composed may be caused to adhere and agglomerate firmly witheach other in groups. Thus the carbon black may be coverted into small10 spherical granules of apparent density in bulk higher than beforesuch treatment, of relatively tenacious structure, with each of suchgranules presenting a more or less polished, non-adherent surface.Carbon black in this spherical grain 15 form possesses all of theadvantages of convenience in handling and distribution above discussedand, in addition, it disperses perfectly in rubber mixtures, and isotherwise as useful or more useful in rubber making and other industries20 1,

than the compressed carbon black of commerce formerly employed. y

I Similarly we have found that a number of other fine, dry powders,among them, all of the carbon pigments commonly known as lamp blacks,zinc oxide, iron oxide and clay, (previously re-' duced to the requisitestate of sub-division ,if necessary) have the property of agglomeratingunder determinable conditions of mechanical manipulation and that when,subjected to suitable turbulent pressure they may be converted. intosmall, tenacious spherical granules-of concentric shelled structure andhaving non-adherent surfaces.

The powders which display this behaviour have certain othercharacteristics. which serve to differentiate them from those powderswhich cannot be agglomerated by such treatment. For example, if jiggedon a vibrating surface, they will agglomerate into small spheres of veryfragile 40 structure, they will form an adhesive lump when squeezed,they will adhere to metallic or nonmetallic ,rods when these areforcibly drawn through them and they are free from gummy and resinousingredients. The present invention has to do with fine powders orpigments having these properties or characteristics and for convenience.they will be termed herein as "agglomerative powders". The powderslisted above are typical but this list' is far from complete and thosementioned are named as illustrating but not limiting our claims for thisinvention as applying to all agglomerative powders.

-We have discovered that by subjecting them to the proper conditions ofturbulent pressure and to proper manipulation, these agglomerativepowders may be converted into granules of greatly increased apparentdensity, having in many instances internal structures of sphericalshells concentrically disposed about central cores, with each granulepresenting a smooth, polished. nonadherent and non-coherent exteriorsurface. The self-generated spherical granules thus produced are ofappreciable mechanical strength and, since they have the property ofwithstanding very considerable direct pressure, they may be handled ortransported in bulk with practically no disintegration. The powder,converted into this spherical-grain form, is-substantially dustless,

free-flowing and non-adherent.

The proper conditions of turbulent pressure necessary for the conversionof agglomerative powders into such spherical granules may be created bythe use of various types of mechanical apparatus. Examples of suitableapparatus are disclosed in our pending applications Serial Nos. 642,850and 40,438. We have found that. lmder certain conditions, we candirectly convert fine agglomeratlve powders from their loose, seeminglyamorphous form into this dense, spherical.- grain form. However theprocess is usually more rapid, economical and commercially eflicient ifa priming charge of pre-formed spherical material is mixed with thepowder being treated. This priming material may be either the same ordifferent from the powder. If such a priming charge is not used, thefirst effect of turbulent pressure on the powder may be to cause thegradual formation of a small number of nuclei consisting of a turbulenteffect of the mechanical apparatus used and thereby accelerates theconversion from powder to dustless spherical asglomerate. (2) Itprovides immediately bodies of. much larger weight than the weight ofthe particles of dust.

. These larger bodies, by collision, provide impacts on the dustparticles of sufllcient intensity to cause permanent adhesion. They alsowiden the zones of eiiective action in the apparatus and so permit theuse of greater clearances than would otherwise be the case, therebysimplifying the mechanical construction of the apparatus.

There are a number of ways of producing satisfactory priming chargematerial but all are alternative methods for accomplishing two purposes;first, exerting sumcient pressure on the powder particles to form firmadhesions: second, reduction of the agglomerates thus formed to aconvenient and suitable size and with three appreciable dimensions. Forexample, satisfactory cores may be secured from some agglomerativepowders by subjecting relatively thin layers of the powders to directcompression, suiliciently heavy to cause the formation of a chunk, cakeor briquette. This, if then rubbed through a wire screen of suitablemesh, is partially disintegrated and the resulting product of thistreatment is suitable, for core material and may be readily built upinto spherical form by the addition of concentric external layers orshells.

As another example. spheres offoreign mate-' rial of suitable densityand size, may be mixed with the agglomerative powder and the mixturesubjected to turbulent pressure. The powder will then form asubstantially ormcentric, spherical shell on each sphere. If thecompodte spherical granules thus formed are rubbed upon a screen of theproper mesh to exclude the original spheres,

they will break and fragments of the shells passing through the screenwill be found suiilciently dense and adhesive to serve as primingmaterial for the subsequent agglomeration of powders of their ownnature. Examples of spheres suitable rorthismn'p e areilneshotorseeds,suchas those of the beet, clover or petlmia.

Likewise, composite granules may be formed by using cores made from onepowder with shells formed from an entirely diilferent powder for usewhere a free-flowing dustless mixture of two or more such powders iscommerically desired.

An important feature of ouainvention lies in our discovery oi. the factthat we are able to take these small agglomerates, which may be so lineas to partake of the characteristics of dust, and T build them, throughsuccessive addition of shells,

toasize thatimpartstothe product thecommerclal advantages above vim,dustlessness, high density, low mass viscosity, spherical shape andnon-adherent surface.

Another important feature of our invention lies in our discovery of thefurther fact that we can alter and control the degree of surface polishimparted to the granulm since, under proper conditions, this is afunction of time of treat-.

ment.

Our ability to control the degree of surface polish enables us:

1. To control the viscosity of the material in bulk, thus facilitatinghandling.

2. To oii'set the increase in viscosity in bulk which would otherwisenaturally accompany increase in average diameter of the individualspheres.

Thus, abilitytocontrolpolishenablesusto maintain adequate turbulentthroughout a wide range of average sphere diameter and thus to add agreater number of concentric shells and produce larger and more usefulspherical agglomerates.

Since-theimpacts deliveredbyonesphere toanother are a function cf-theweight of the spheres,'it becomes possible to increase rapidlythedensityoftbesphericalgranuluinprocess of treatment by employingaprlming chu-geof,

large spheres. We may, by propermanipulation and adequate time oftreatment. this cause the density ofthegranulestoapproachtheabdolutespecific gravity of the material being treated.'Ihisisanothercharacteristicandextremelyimportant feature of ourinvention.

For of ustratmtbeinventionwill nowbemorew w r descrlbedascarriedoutinconnectionwiththeofspherical s ain carbon black. In the drawing, I 7

Fig.1 reprmtsspherlcflgmincarhmblack seen' in the field of a microscope.mlnlfled diameters;-Fig.2representsspherlcalgrainsincouidethegranulesbeingshownincrosssectionintheileldof amicroseopamagniiieddo diameters cores may be first producedseparately by subjecting the seemingly amorphous powder to prolongedtreatment under conditions of adequate turbulent pressure. The cores 1thus produced present a smooth, non-adherent surface and mayconveniently have an apparent density in bulk of more than 12 pounds percubic foot, for example, about 20 pounds per cubic foot. The averagesize of these cores, as measured by sieve tests, is determined by thedegrees of turbulence and pressure to which the powder is subjected. Theoptimum size is determined by the number of concentric shell-like layerswhich are subsequently to be added to the core and by the design of theapparatus in which the additions are made. For carbon black, an averagecore diameter ranging from 300 mesh to 60 mesh has been foundsatisfactory.

Substantially equal amounts of these cores and of commercial carbonblack may now be introduced into an apparatus such, for example, as thatdisclosed in our pending application Serial No. 642,850 or 40,438. Thisapparatus comprises a drum which constitutes a. container and in whichare arranged a plurality of impelling elements and baflie elementsmovable past each other in an approaching and receding manner andprovided with means to cause also an up-and-down circulation in the massdelivered thereto. The composite charge may be thus subjected topressure and to turbulence causing this pressure to be multi-directionalupon each particle thereof. This is accomplished by .a sliding orshifting action of the mass upon itself under conditions of turbulenceand pressure and a stroking or polishing interaction of its particles.Under these conditions there occurs an agglomeration of the flocculentcarbon black upon the cores or fines with the result that a sphericalshell is built up upon each core.

In Fig. 4 of the drawing is shown a core l0 upon which has been formeda. concentric shell II. This figure represents a single granule ofspherical-grain carbon black at high magnification, the core being shownin elevation and the concentric shells in section.

The process may be continued until all of the fiocculent carbon blackhas been agglomerated upon the cores in the form of spherical shells andifthe components of the initial charges are substantially equal, it isapparent that each shell willcomprise substantially 50% of the weight ofthe spherical grain thus formed. It is desirable to continue the processfor a time after the disappearance of the fiocculent carbon black fromthe apparatus suflicient to polish the surfaces of the spherical grains.At this stage the entire charge has been converted to spherical granulesof high apparent density, the individual granules being suficientlytenacious to stand such pressures as they may be subjected to inhandling, and presenting a more or less polished nonadherent surface. Ifthe process is continued further, the granules tend to become more andmore dense and to bereduced in diameter. The process may be stopped whenthe spherical granules have thus reached a convenient commercial densityand polish.

We have described the production of spherical granules comprising a coreand a single con-' centric shell by a single regenerative processterminating when an equal weight of flocculent carbon black has beenagglomerated upon each core. If desired, a new charge of flocculentcarbon black may now be introduced into the apparatus and, as before,.this may approximately equal in weight the amount of the sphericalgrain charge already produced or remaining therein.

The process is now renewed as before and a second concentric shellagglomerated upon the outer surface of the first. Such a second shell isindicated by reference character I! in Fig. 4

of the drawing. When the flocculent carbon black of the charge has againagglomerated, the process may be repeated. In Fig. 4 a third concentricshell I3 is shown and in Fig. 2 are shown Fig. 1 representsspherical-grain carbon black.

or of other agglomerative powders as seen in the field of a microscopein the magnification of 50 diameters. It will be noted that all thegrains are spherical or substantially so and that there is asubstantially uniform upper limit of diameter which has been attained bya large number of the granules. The smaller granules represent thosewhich contain in their composition a smaller number of concentric shellsthan the larger granules, or the shells of which are thinner.

We have found that in the case of carbon black subjected to treatment inthe type of apparatus described in our pending application Serial No.642,850 or 40,438, it is best to use a priming charge not coarser than60 mesh if an increment of equal volume is to be added in the form of ashell, because the resulting spherical grains produced by such anincrement will then have a size of about 40 mesh and using carbon black,we have found that the subjection to turbulent pressure of a charge ofspherical grain carbon black containing a substantial percentage ofgrains substantially larger than 40 mesh in the type of apparatusdescribed, results in viscosities and pressures so great as to crack andburst the granular agglomerates, thus impairing the free-fiowing anddustless characteristics of the charge., For this reason, when treatingcarbon black by the above process, we have found it advantageous tostart with a'priming charge in the range of 150 mesh so that a largenumber of concentric shells could be added before reaching the limitingsize.

. As the diameter of the spherical grains increases with the addition tothem of successive increments of carbon black, and also as theapplication of turbulent pressure is continued after all the fiocculentcarbon black has been applied to the cores of the priming charge, someof the shells become ruptured into fragments but not into dust, andthese fragments, in the presence of their neighbors, round off andbecome to all intents and purposes new core material. This processcontinues throughout the run and results in a decrease of the averagesize of the agglomerates with time of running. It is also to be thesmaller agglomerates from the mass so that they maybe used as primingmaterial for new charges, and retaining in the finished product onlyagglomerates of the larger sizes.

In the light of our present knowledge, we may suggest one theory of whattakes place within the drum to cause the carbon black to assume its newand relatively dnse form by reference to Figs. 5 and 6 of the drawing.v'Il'ie station ary elements 42 are arranged alternately with the movingelements. 32 and the charge of black surrounds and entirely fills thespace between these elements. As the elements 32 move relative tothe"elements 42 (Fig. 5), they tend to carry the black in a masstherewith'but such movement... of the black is opposed by'the stationaryelements 42. The result is that cones 86 and 81 of black form bothforwardly and reawardly of the elements 32 and move along with theseelements, while cones "and 89 of black form both forwardly andrearwardly of the elements 42 and remain stationary therewith; Thecarbon black intermediate the elements 32 and 42 (indicated by line 90of black particles in Fig. 5) is in a state of turbulence, the blackadjacent to the elements 32 moving nearly as fast as those elements andthe carbon black adjacent to the elements 42 remaining nearlystationary. The relative positions of the elements are constantlychanging as the elements 32 approach and recede from the elements 42and, due to this action, the particles of carbon black are alternativelybeing brought into most intimate and bombarding re-' lation whereby theyare compacted into the relatively dense form of the finished product andinto a relatively loose relation, wherein they are free to rearrangethemselves for the next impact. Thus the black particles areintermittently subjected to pressures or impacts and are relattvelyrearranged between the successive impacts,

suchimpacts or pressures thereby becoming multi-directional, i. e., notocciu'ring twice in suc cession in the same direction..

If the cores are' formed from compressed or briquetted material, we havefound it advanta geous to subject the rough fragments resulting fromthis method to turbulent pressure for a 'short period. This treatmentbreaks .off the rough irregular projections of such cores, tends toequalize the three dimensions, fills in the cavities with the detritusresulting from the abrasion of the projections and thus produces coreswhich are more nearly perfect spheres. This condition is desirablebecause the more nearly spherical the priming charge, the lower theviscosity of the subsequent mixture with the agglomerative p'owder.Lower viscosity, within limits, enhances .the turbulent pressure effectsof our apparatus and thus assists the conversion process. If the core isspherical to start with, the shell agglomerated thereon will also bespherical. If the core is irregular'in its shape, the shell .will not beperfectly spherical but will tend to approach spherical shape morenearly than the core. In Fig. 3

is shown a core ll of more or less irregular shape, such as mightbe'found by the compressing and breaking process, and-upon this has beenformed a shell l5. This, it will be noted, tends to fill in and smoothout the surface irregularities of the of sectioning the sphericalgranules. -As above suggested, the cores 20 may be of zinc oxide or theymay be of carbon black or other agglomerative powder.

The limiting size of the agglomerates depends somewhat upon the designand operation of the agglomerating apparatus used for producing therequisite turbulent pressures, but is even more dependent upon thenature of the agglomerative' powder being treated. Zinc oxide, forexample, can be caused to agglomerate by increments into spheres oflarger than 20 mesh before the result ing increased pressure exceeds thestructural resistance of the spherical grains and break down into dustensues. i

The continuous tendency toward the replacement of fine material as theprocess is carried out is advantageous for two reasons:

1. It maintains the distribution of particle sizes.

2. It affords a continuous replacement of finematerial for the start ofnew cycles if these fine particles are screened out at the end of eachrun, thus removing the necessity for a separate and distinct process orstep for the production of cores.

' The distribution of particle sizes is important to the process forthree reasons:

1. It decreases the viscosity of the charge by providing .supportingsurfaces in the interstices between the larger particles, thusincreasing the ability of the apparatus to produce adequate turbulentpressures.

2. It decreases the liability of the material to be rupturedor crushedby conveying, transportation, or handling, thus inhibiting the prematurereturn of the spherical grains to their. original, dusty finecomponents.

' 3. It increases the apparent density in bulk of the commercialproduct. over that which would obtain if only one size of particle werepresent, 1

thus economizing on packing materials and stor-- ,terial necessary oradvisable in the charge is a function of the combined viscosities of thepriming material and the fine powder. From this it follows that it ispossible to use a 5% or 10% priming charge in treating certain powders,whereas a 33% priming charge may be required in treating other finepowders. In the case of carbon black, 9. 33% priming charge is theminimum below which it is not convenient to go.

This application is a division of our application Serial No. 684.884,filed August 12, 1933 which issued as Patent No. 1,957,314, which inturn was a continuation-in-part of our earlier application Serial No.623,184, filed July 18, .1932, and corresponding to our Canadian PatentNo. 333,741, granted July 4,1933. Patent No. 1,957,314 has now beenreissued as Reissue Patent No. 19,750, November 12, 1935.

Having thus described our invention, what we claim as new and desiretosecure by Letters Patent is:

1. As a new product of manufacture, polished spherical granules eachcomprising a tenacious core of one .agglomerative powder enclosed in aplurality oi. concentric shells of another agglomq erative powder, allunited in an integral body of sufiicient tenacity to withstanddisintegration when handled in bulk.

2. As anew product of manufacture, polished spherical granulescomprising in their structure a tenacious core and a concentric shell offine dry agglomerative powder united thereto with suificient tenacity towithstand disintegration when. handled in bulk, and of the core andshell one 10

